BOSTON -- A federal judge declared a mistrial on Monday in the case of a former Needham doctor and nurse practitioner who are accused of illegally distributing pain medications to drug users.

Judge Patti Saris declared the mistrial after the jury failed to reach a verdict in the case against Dr. Joseph Zolot and Lisa Pliner.

"We are disappointed that the jury did not reach a verdict," U.S. Attorney Carmen M. Ortiz said in a statement. "It is our intention to retry the case."

According to court reporter Lee Marzilli, the jury said in a note to the judge that one juror was unable to conscientiously change their vote. As a result, the jury was deadlocked on all charges.

Howard Cooper, a defense attorney for Zolot, said in a phone interview that he was "not surprised" the jury deadlocked due to the complexity of the case.

The case involved difficult medical issues, Cooper said, "and in that regard I suppose it's not surprising that any jury would have a difficult time grappling with them and trying to resolve them."

"My view is that this case is not an appropriate case for criminal prosecution for precisely that reason," he added.

A lawayer for Pliner called the mistrial "unsatisfying."

"My client has been living under the cloud of an investigation and then an indictment that has been ongoing for over seven years, and we hoped that today would be the day that she would put it all behind her," defense attorney Michael Connolly said.

Zolot and Pliner allegedly conspired with each other to prescribe painkillers to patients without a legitimate medical purpose for their own financial gain.